Process for stabilizing rubber containing copper against oxidation



3 2,923,752 PROCESS FOR STABILI'ZING RUBBER CONTAIN- ING corrnn AGAINST OXIDATION Boris Nicholas Leyland and Ronald Lee Staiford, Manchester, England, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain No Drawing. Application December 22, 1955 Serial No. 554,612

Claims priority, application Great Britain December 31, 1954 3 Claims. (Cl. 260-752) This invention relates to rubber antioxidant mixtures and their application to natural rubber in order to protect the rubber against deterioration by oxidation both before and after vulcanisation, especially in the presence of copper or manganese.

According to the present invention we provide a process for protecting natural rubber against deterioration by oxidation, especially in the presence of copper or manganese, which comprises incorporating into the rubber, at any suitable stage before curing, at least one mercaptoarimidazole and at least one N:N-disubstituted 'diaryl; alkyl, aryl; or cycloalkyl, aryl p-phienylene diamine.

The mercaptoarimidazole may be used as such or in the form of its metal salt, for example its zinc, magnesium or calcium salt. azole is 2-mercaptobenzimidazole but others may be used, for example 2:2'-dibenzimidazyl disulphide.

,We are aware that it has already been proposed to use mixtures of antioxidants generally, and in particular, phenyl-u-naphthylamine and phenyl ,B naphthylamine, with mercaptoarimidazoles in order to enhance the antioxidant effect. However it has not hitherto been observed that any special efi'ect with respect to oxidation in the presence of copper or manganese is obtained and it has not been proposed to use mixtures of'the N:N'-disubstituted p-phenylene diamines of our invention with mercaptoarimidazoles. We have discovered that such mixtures have an unexpected, outstanding effect on the oxidation of natural rubber in the presence of copper or manganese and our present invention is based upon this discovery.

Suitable N:N'-disubstituted p-phenylene diamines include N:N'-di-/3-naphthyl-p-phenylene diamine, N:N'-dia-naphthyl-p-phenylenediamine, N:N-diphenyl-p-phenylene diamine. N-cyclohexyl-N'-phenyl-p-phenylene diamine, N-sec.butyl-N'-5-naphthyl-p-phenylene diamine and N:N-dicyclohexyl-p-phenylene diamine.

The proportion of mercaptoarimidazole to be used in the process of this invention may be from about 50% to about 200% of the weight of the N:N'-disubstituted pphenylene diamine; preferably the proportion is about 100%.. Theamonnt of the combined agents used in the" rubber is conveniently from 0.5% to 4.0% of the weight; of the rubber hydrocarbon.

The efiicacy of the process of this invention may be even further enhanced by the further incorporation into the rubber of a copper-sequestering agent, for example ethylene diamine tetracetic acid or a metal salt thereof, disalicylal alkylene diamines, S-hydroxy-quinoline or p aminophenol. Suitable proportions of the agents are from 3% to 10% of the total weight of the copperinhibiting system.

The agents may be added to the rubber mix singly or inv combination. In the latter case it is convenient to use the agents as a preformed mixture and such preformed mixtures of mercaptoarimidazole, N:N-disubstituted p-phenylene diamine and, optionally, copper- The preferred mercaptoarimid-' 2,923,752 I Patented Feb. 2, was

2 sequestering agent form a further feature of this invention.

The invention is illustrated but not limited by the following examples in which parts and percentages are by weight.

Example 1 Vulcanisable rubber compounds were made up by the conventional method according to the following formulae:

Mix

The mixes were vulcanised for 150 minutes at 141 C.

Mi A B o D Time in hours to attain O -uptake of:

Similar compounds as given above, vulcanised and tested in the same way but containing phenyl-a-naphthylamine and phenyl-fi-naphthylamine as anti-oxidants were also made for comparison.

Nlix a b c d Pale crepe rubber Zinc oxide Blane fixe Steuic acid- Sulphur Diphenylguanidine- Copper stearate Phenyl-a-naphthyla nine.

Phenyl-B-naphthylamine... 2-tnereaptobenzimidazole Mix Example'2 The following compounds were prepared in the conventional manner.

Mix E F G H Pale crepe rubber 100 100 100 100 Zinc oxide 10 10 10 10 Blane fixe.-- 75 75 75 Stearie acid. 1 1 l 1 Titanium di 10 10 1O 1O Sulphur 2.0 2.0 2.0 2. 0 Zine diethyldithioearbamate 0. 375 0.375 0.375 0. 375 N :N -di-B-naphthy1-p-phenylenediamine 2 l 1 O. Z-mercaptobenzimidazole 1 0. 9 0. 95 S-hydroxyquinoline 0. 1 p-aminophennl 0. 1 Copper stearate 0. 2 0.2 0.2 0.2

Mix- .T

The following results were obtained;

Mix E t-50% period 9.2 16.0 16.4

Example 3 The following mixes were prepared in the conventional manner:

Mix J These mixes were vulcanised for 30 minutes at 141 C. and the antioxidant effect was measured as in Example 2.

The following results were obtained:

t-50% period in days 8. 2

Example 4 The following mixes were prepared in the conventional manner:

Mix M N P Q R Pale crepe rubber 100 100 100 100 100, Zinc oxide 10 10 1O 1O 10 Blane fixe..- 75 75 75 75 75 Ste'tric acid 1 1 1 1 1 Sulphur. 3. 0 3.0 3. 0 3.0 3.0 Diphenylgua 0.5 0.5 O. 5 0. 5 0.5 Copper stearate 0. 2 0. 2 0. 2 0. 2 0. 2 N:N-di-fl-naphthyl-p-phenylenediamine 2 1 N-cyclohexyl-N-phenyl-p-phenylenediamine 1 1 p-Aminophen0l 0.1 2-mereaptobenzimidazole 1 0. 9

The mixes M and N were vulcanised for minutes at 141 C. and tested by the bomb ageing method discribed in Example 2. The mixes P, Q and R were vulcanised 60 for minutes at 141 C. and tested by the oxygenabsorption method described in Example 1.

The following results were obtained:

Mix M N t-50% period in days 6.0 13. 0

Mix. P Q R Time in hours to attain oxygen uptake of 1.0% 67 101 96 Example 5 The following mixes were'prepared in the conventional manner:

Mix S T U V Time in hours to obtain an oxygen uptake. 54. 5 80. 5 43 93 What we claim is:

1. A process for stabilizing against oxidation rubber, consisting of natural rubber, and copper, which process comprises incorporating into said rubber, prior to curing, a copper inhibiting system in a proportion of from .05% to 4% by weight of said rubber, said copper inhibiting system consisting essentially of (a) From 33% to 66%%, by weight of a mercaptobenzimidazole selected from the group consisting of 2- mercaptobenzimidazole and its metal salts and 2:2-dibenzimidazyl disulfide;

(b) From 33%% to 66%%, by weight, of a member selected from the group consisting of N:N'disubstituted diaryl; alkyl, aryl; cycloalkyl, aryl; and dicyclohexyl pphenylene diamines; and, additionally (c) From 3% to 10%, by weight based on (a) and (b), of disalicylal ethylene diamine.

2. The process of claim 1, wherein said (a) and (b) components of said copper inhibiting system are present in equal amounts.

3. A process as claimed in claim 1, wherein said mercaptobenzimidazole is Z-mercaptobenzimidazole.

page 151, compiled by editors of India RubberWorld, New York, New York. 

1. A PROCESS FOR STABILIZING AGAINST OXIDATION RUBBER, CONSISTING OF NATURAL RUBBER, AND COPPER, WHICH PROCESS COMPRISES INCORPORATING INTO SAID RUBBER, PRIOR TO CURING, A COPPER INHIBITING SYSTEM IN A PROPORTION OF FROM .05% TO 4% BY WEIGHT OF SAID RUBBER, SAID COPPER INHIBITING SYSTEM CONSISTING ESSENTIALLY OF (C) FROM 3% TO 10%, BY WEIGHT, BASED ON (A) AND BENZIMIDAZOLE SELECTED FROM THE GROUP CONSISTING OF 2MERCAPTOBENZIMIDAZOLE AND ITS METAL SALTS AND 2:2''-DIBENZIMIDAZYL DISULFIDE, (B) FROM 331/3% TO 662/3%, BY WEIGHT, OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF N:N''-DISUBSTITUTED DIARYL, ALKY, ARYL, CYCLOALKYL, ARYL, AND DICYCLOHEXYL PPHENYLENE DIAMINES, AND, ADDITIONALLY (C) FROM 3% TO 10%, BY WEIGHT, BASED ON (A) AND (B) OF DISALICYLAL ETHYLENE DIAMINE. 